Question

Which of the following statement is incorrect in a series-series feedback?

• A. Closed loop input impedance increases
• B. Closed loop output impedance increases
• C. It is trans-resistance amplifier
• D. Input is voltage

Hint:

Remember the impedance rules for feedback:
Series at input $\rightarrow$ Input impedance increases.
Series at output $\rightarrow$ Output impedance increases.
Thus, Series-Series feedback increases both input and output impedances.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The problem asks to identify the incorrect statement among the options describing a series-series feedback configuration.

Step 2: Key Formula or Approach:
In a Series-Series feedback amplifier (current-series feedback):
- Input feedback is connected in series (mixes voltage).
- Output feedback is connected in series (samples current).

Step 3: Detailed Explanation:

• Input Impedance: Series mixing at the input increases the input impedance by a factor of $(1 + A\beta)$. Therefore, statement (A) is correct.

• Output Impedance: Series sampling at the output increases the output impedance by $(1 + A\beta)$. Therefore, statement (B) is correct.

• Type of Amplifier: Since the input is a voltage and the output is a current, the basic gain of the amplifier is a trans-conductance ($G_m = I_o / V_{in}$). Thus, it is a trans-conductance amplifier, NOT a trans-resistance amplifier. Thus, statement (C) is incorrect.

• Input Quantity: Since the feedback is in series with the input, the input signal is a voltage. Therefore, statement (D) is correct.

Step 4: Final Answer:
The incorrect statement is that it is a trans-resistance amplifier, which matches Option (C).